An optical disk device capable of reading and writing information from and on a disk such as a CD, a CD-ROM, and a magneto-optical disk has been widely adopted due to fast accessing to desired information. Also, an MD (Mini Disk) having a smaller disk diameter has been spreading rapidly in recent years due to its easy handling, replacing compact disks and cassette tapes.
In personal computers equipped with a magneto-optical disk device as an external information recording/reproducing device, a portable notebook type has been drawing an attention. Also, a portable type MD for allowing the user to enjoy music outside has been a focus of an attention as well. Thus, in both personal computers and MD, portability is of a great importance, and therefore a demand for thinner and smaller optical disk device has been increasing.
Incidentally, main mechanical components of an optical disk device include a loading mechanism for transporting a cartridge holder holding a cartridge encasing a disk to a predetermined position, a spindle motor for mounting an optical disk so as to rotatably drive thereof with a predetermined rotation speed, an optical head for projecting a laser light onto an optical disk so as to record and reproduce information, an optical head transporting mechanism for controlling and transporting the optical head to a predetermined position on the optical disk, and other mechanisms.
In the loading mechanism, a cartridge held in the cartridge holder is laterally moved, and after transporting the cartridge so that a chucking target section of the optical disk is above a chucking section of the spindle motor, the cartridge is lifted downward towards the spindle motor. A main chassis having the spindle motor and the optical head is provided with cartridge position determining pins which place the cartridge in a predetermined position. The optical disk is provided with a center hub made of a magnetic material, and in a vicinity of the chucking section of the spindle motor, a disk chucking magnet is fixed. The optical disk is held on the chucking surface of the spindle motor by the magnetic force of the chucking magnet.
In the optical disk device having the described arrangement, since it is required to move the cartridge in the vertical direction with respect to the spindle motor fixed to the main chassis, it is required to provide a space in the optical disk device for the movement of the cartridge. The cartridge is slightly larger than the optical disk encased therein. For example, in an MD, while a disk diameter is 64 mm, the cartridge has dimensions of 68 mm.times.72 mm. Also, the cartridge has a thickness of 5 mm, and normally, substantially 3.2 mm of space is required for the vertical movement of the cartridge required for mounting of the disk onto the spindle motor.
The magneto-optical disk and MD are encased in a cartridge for easy handling; however, the vertical movement mechanism of the cartridge can be a problem in realizing a thinner optical disk device.
In order to overcome this problem, for example, Japanese Unexamined Patent publication No. 57431/1995 (Tokukaihei 7-57431) discloses an arrangement wherein instead of moving the cartridge in the vertical direction, the cartridge is laterally inserted with respect to the cartridge holder fixed on the side of the main chassis, and the spindle motor is lifted upward in accordance with the loading operation so as to chuck the disk onto the spindle motor.
The diameter of the spindle motor is set so that the spindle motor does not interfere with a chucking region of the disk which is specified and the optical head positioned for recording and reproducing information on and from the innermost side of the disk. In an MD, the diameter of the disk chucking surface is set to 16 mm. Thus, the space required for the loading operation for chucking of the disk onto the spindle motor is significantly smaller when the spindle motor is moved in the vertical direction, compared with the case of moving the cartridge in the vertical direction.
FIG. 2 shows an arrangement of the spindle motor. The arrangement of FIG. 2 is a cross sectional view of a brushless motor which is generally referred to as an axial gap type or a surface facing type. A motor fixing section has an arrangement wherein a bearing holder 213 is fixed to a motor chassis 215, and bearing 214 is press-fit in the bearing holder 213, and a stator coil 212 is provided around the bearing holder 213 on a motor chassis via a flexible substrate 211. On the other hand, a motor rotating section has an arrangement wherein a rotation shaft 203 is press-fit on the center of a turn table 204 on which the disk is placed, and a rotor magnet 205 is provided around the rotation shaft 203. On the turn table 204, a disk chucking magnet 207 is fixed. Between the rotor magnet 205 and the turn table 204, a thin iron plate made of a magnetic material is sandwitched as a back yoke 206. The motor chassis is made of a magnetic material such as iron, and serves also as a back yoke on the coil side. In order to avoid a direct contact between the turn table 204 and the bearing holder 213 during rotation of the turn table 204 so as to ensure smooth rotation, a sliding section 209 is provided. Also, in order to prevent the rotation shaft 203 from coming off the bearing 214, the end portion of the rotation shaft 203 is engraved, and a washer 208 is attached around the groove. The rotor magnet 205 is divided into a number of regions in the circumferential direction, each of which is magnetized with a north pole and a south pole in a direction of the thickness in an alternating pattern.
FIG. 3(a) and FIG. 3(b) respectively show a magnetization state of the rotor magnet 205. Here, the rotor magnet is magnetized with 12 poles.
FIG. 4 shows an arrangement of the stator coil 212. Here, nine coils are provided around the bearing holder 213, and (1) coils 212a1, 212a2, and 212a3, (2) coils 212b1, 212b2, and 212b3, and (3) coils 212c1, 212c2, and 212c3 are connected in series, respectively.
In a magnetic circuit gap composed of the rotor magnet with back yoke and the back yoke on the stator coil side (motor chassis), the stator coil is provided, and a current is sent to each coil, and by carrying out, for example, a three-phase half wave current control, the rotation of the turn table is controlled.
As mentioned above, one of the effective means for realizing a thinner MD device is to lift the spindle motor, not the cartridge, when chucking the disk onto the spindle motor. However, lifting of the spindle motor in this manner has a limit when an optical disk device with an even thinner thickness is demanded. Assuming that the cartridge is moved only in the lateral direction when loading is carried out, and the lateral movement of the cartridge is barely made above the upper surface of the turn table of the spindle motor having a thickness of hi, in the spindle motor, the thickness h required from the lower surface of the cartridge to the lower surface of the optical disk device is minimized when h=h1. In the case where other components of the MD device, for example, the optical head is made thinner than the spindle motor, the height to the lower surface of the spindle motor determines the height to the lower surface of the optical disk device, namely, the height to the lower surface of the spindle motor becomes one of the factors determining the total thickness of the optical disk device. Therefore, it is required to make the thickness of the spindle motor thinner.
Other mechanical components of the optical disk device include, other than the described mechanical components, magnetic field applying means for applying a supplementary magnetic field to a laser light converged position of the medium.
The magnetic field applying means, for example in the MD device, have a magnetic head section composed of a slider member made of resin having a core section provided with coils. The magnetic head section is attached to the tip of an elastic suspension member so that the magnetic head section is in a sliding state when rotating the disk. The suspension member is fixed to a supporting arm integrally extending from a light pickup. This arrangement allows the suspension member to be moved in the radial direction of the disk integrally with the light pickup.
Also, the magnetic head section, being in the sliding state, can be moved upward from the disk, namely, the magnetic head section can be moved in a direction so that the distance between the core section and the disk surface increases. Further, the magnetic head section can be held above the cartridge.
When the cartridge is inserted into the optical disk device, the loading mechanism laterally moves the cartridge held in the cartridge holder towards the inside. Here, the magnetic head section is held above the cartridge by the magnetic head lifting mechanism so as to avoid contacting the cartridge being inserted.
As described, the cartridge is placed in a predetermined position by the loading mechanism. Also, the magnetic head section held above the cartridge is lifted downward towards the disk surface by the magnetic head lifting mechanism.
In this manner, the magnetic head section is held above the cartridge so as to avoid contacting the cartridge when loading. This further increases the thickness of the optical disk device, presenting a serious problem in realizing a thinner and smaller optical disk device.
As a countermeasure, and as a method for realizing a thinner optical disk device having the magnetic field applying means, a method (referred to as Method 1) of retreating the light pickup integrally fixed to the magnetic head section outside of the moving region of the cartridge is available. In this method, instead of retreating the magnetic head section above the cartridge, the magnetic head section is retreated to a position adjacent to the cartridge when viewed from the top.
However, in Method 1, the following problem is presented. That is, in order to make the optical disk device thinner, the distance between (1) the objective lens for converging the laser light on the medium surface and (2) the medium is required to be small. For this reason, in general, the cartridge is provided with a window for effectively converging laser light on the medium, and the objective lens of the light pickup is designed so that the objective lens moves into the window of the cartridge whose position has been determined. Also, in some cases, an objective lens actuator for controlling the position of the objective lens partially moves into the window of the cartridge.
For this reason, after the position of the cartridge has been determined, when the light pickup in the retreat position is moved above the medium in order to access the recording medium which has been set, the objective lens and the objective lens actuator collide with the wall of the cartridge constituting the window. Thus, as in Method 1, when the light pickup is retreated outside the moving region of the cartridge, the objective lens of the light pickup cannot be moved into the window of the cartridge, and it becomes impossible to narrow the distance between the objective lens and the medium. This presents a problem that the optical disk device cannot be made thinner.
As another method for realizing a thinner optical disk device, a method (referred to as Method 2) disclosed in Japanese Unexamined Patent publication No. 91850/1988 (Tokukaisho 63-91850) is available. In Method 2, as shown in FIG. 78, the magnetic head section 103 and the light pickup 102 are provided separately as non-integrated units. In FIG. 78, members 101, 105 and 106, 107, 108, and S101 to S105 respectively represent the spindle motor, the driving motors, an encoder, a controlling circuit, and switches. When the light pickup 102 is subjected under tracking control in the radial direction of the disk 104 so as to be moved, the magnetic head section 103 is controlled such that the magnetic head section 103 is moved for the same amount the light pickup 102 has moved. Here, prior to loading the cartridge, the magnetic head section 103 is retreated to the retreat position so as to avoid contacting the cartridge, and after loading the cartridge, the retreating of the magnetic head section 103 is released, and the magnetic head section 103 is placed in a position facing the light pickup 102 via the disk 104.
In Method 2, contrary to Method 1, the light pickup is not retreated. Thus, the light pickup does not collide with the wall of the cartridge constituting the window, thus allowing the objective lens of the light pickup to be moved into the window of the cartridge.
However, Method 2 has the following problem. That is, the position of the light beam spot converged by the light pickup on the disk is always changing in accordance with the tracking position control. In order to carry out recording and erasing of information under this condition, it is required that the region (supplementary magnetic field applied region) to be applied with a magnetic field for recording and reproducing by the magnetic head exactly coincides with the position of the light beam spot.
The supplementary magnetic field applied region has a characteristic of depending on an area facing the disk (core area) of a magnetic head core section.
Here, in order to improve the rising characteristic of the applied magnetic field, it is required to reduce the inductance of the coils. Thus, the core area cannot be made larger; consequently, the supplementary magnetic field applied region becomes small. Therefore, it is required to always accurately carry out, with respect to the small supplementary magnetic field applied region, positioning of the light beam spot which is changing constantly. For this reason, when the magnetic head section and the light pickup are provided separately as non-integral units as in Method 2, a problem is presented in that the positioning of the magnetic head section on the light pickup becomes difficult.